1. Field of the Invention
The present invention relates generally to the field of self-contained breathing apparatus, and more particularly to closed-type, oxygen breathing apparatus.
2. Prior Art
Various types of apparatus are known for enabling a user to live and function in hostile atmospheres containing poisonous materials or containing insufficient oxygen to sustain life. One familiar example of such apparatus is the pumped air system used by suited, underwater divers.
Currently more common are portable, Aqua-lung or SCUBA (Self Contained Underwater Breathing Apparatus) gear used by free divers and in similar form, by fire fighters in many hazardous situations. Typically, SCUBA-type apparatus employ a relatively large compressed air tank, a mouthpiece or face mask being connected to the tank through a flow regulator-usually of a demand type. With such apparatus, users inhale from the tank and exhale into the ambient atmosphere.
Currently, there exist requirements in the United States by MSHA (Mine Safety and Health Administration), that portable lightweight, self-contained emergency breathing apparatus, having at least one hour capacity, be provided for all underground users in this country. SCUBA-type breathing apparatus, which may be considered "open" systems because users exhale into the ambient, are generally unsatisfactory for such an application because of the relatively large size and weight of the apparatus necessary to provide a one hour breathing capacity. Consequently, alternative, more compact and light weight, breathing apparatus are preferred for applications requiring relatively long breathing capacity.
Some types of portable oxygen breathing apparatus are constructed to provide breathable oxygen generated as a chemical reaction product, thereby ordinarily eliminating the need for pressurized oxygen tanks. However, because of the type of chemical reactants used, such apparatus tend to be considered potentially unsafe. To applicant's knowledge, no oxygen-generating breathing apparatus for one hour duration have been approved for emergency use by NIOSH (National Institute for Occupational Safety and Health) and MSHA (Mine Safety and Health Administration).
Portable oxygen breathing apparatus are more typically constructed to use gaseous oxygen from one or more pressure tanks. In some systems a user breathes from the tank and exhales into the atmosphere; however, this is wasteful of the oxygen. Preferably, closed systems are used in which oxygen from a tank is mixed with a user's exhaled breath before breathing. Scrubbers or chemical absorbers are provided to reduce the concentration of exhaled carbon dioxide to an acceptable level. Ordinarily in such closed-type systems pre-breathing mixing of pure oxygen and scrubbed, exhaled breath is accomplished in a flexible bag.
However, heretofore available closed oxygen tank breathing apparatus have, for various reasons, not been entirely satisfactory; hence, substantial improvements are required to provide the safe, reliable emergency breathing apparatus required for life endangering situations. For example, some heretofore available closed oxygen apparatus have had relatively exposed, and hence relatively easily damaged, mixing bags. Also, many known apparatus are constructed so that a user inhales, as well as exhales, through the carbon dioxide scrubber, thereby permitting excessive amounts of unabsorbed carbon dioxide to be inhaled.
Some available types have relied, to obtain one hour breathing capacity, upon low oxygen flow rates, thereby requiring complicated and expensive demand regulators. Other types have been constructed as "throw away" apparatus and are relatively expensive, since they are non-replaceable after use. In addition, these "throw away" apparatus cannot be periodically serviced or recharged as may be necessary to maintain required high levels of reliability.
For these and other reasons, applicant has invented a greatly improved, closed-type, oxygen breathing apparatus in which, for example, the breathing bag is protected against damage and in which danger of rebreathing exhaled carbon dioxide is substantially eliminated.